Unlocking Your Old Carrier-Locked Japanese iPhone to Use with a Cheap SIM

Greg Lane
BIG DISCLAIMER! Try this at your own risk. We don’t guarantee that any of this will work for you and we’re not responsible if it ends up costing you money.

Until May 2015, if you got an iPhone from au, DoCoMo or Softbank in Japan, the phone was locked to the carrier. Try as you might, with “jailbreaking” or other software-based unlocking techniques, it was impossible to use a SIM from another provider in your iPhone. These days, it’s possible to get your iPhone (and many other phones/devices) unlocked by your carrier, but generally only those that were bought after May 2015, and only if they are newer models. The process can be quite bureaucratic, too.

Luckily, with a little bit of hackery that virtually anyone can do, you can unlock your old handsets yourself.

Why would you want to do this?

Because it’s so much cheaper and less restrictive, and if you’ve got an old off-contract iPhone lying around, why not re-purpose it for the kids or a visiting relative? Check our guide to cheap Japanese SIMs to see what it will cost you. Most of the contracts listed in that article are 12 months, some are 6, and for a few, you can cancel whenever you want. Better still, unlike the mega-big carriers, they don’t automatically renew and then charge you 10,000 yen or more to cancel your contract. Personal note—Y-Mobile and au, I hate you both for charging me 10,000-yen cancellation fees for contracts that had automatically renewed.

unlocking a japanese iphone
au, SoftBank and DoCoMo aren’t the only players anymore. | Photo by Greg Lane

Considerations before you begin

1. Check your current contract

If your phone is currently under contract, the first port of call is your local au/SoftBank/DoCoMo store to find out how much time you have left on your contract and when you can cancel it (and at what cost). Big carrier contracts are typically 24 months long with a one-to-two-month window at the end during which you can cancel it without charge. If you miss the window, your contract will be automatically renewed for another 24 months, and you’ll incur big charges to cancel it. Amazingly, these are waived when you buy an expensive new phone—but that’s just their way of keeping you in their mobile prison.

2. Find out if your iPhone is actually carrier-locked

The Japanese Government decided to crack down on the anti-competitive practice of phone-locking with a new law enacted in May 2015. This hasn’t stopped the big carriers selling carrier-locked handsets, but the difference is, if you ask them to unlock your phone, they must comply. Sadly, as we mentioned above, this doesn’t apply to phones sold before the law came into effect.

unlocking a japanese iphone
This is what you’ll see if you put another company’s SIM in your carrier-locked handset. If you see this during the process below, try starting again. | Photo by Greg Lane

3. Make sure your phone is compatible with the MVNO SIMs

My personal experience is with an iPhone 4S. It will almost certainly work for later models, but it may not work for older iPhone 3GS handsets. If you’re not sure, I’d suggest going down to BIC Camera and asking them if you can use an MVNO SIM in your old handset. Don’t tell them it’s carrier-locked though—tell them you brought it with you from overseas land. If you mention “carrier locked” they will refuse to reason with you.

So tell me how to unlock my iPhone already!

The technique is very simple, but a little bit finicky. To unlock your phone, you need a “Turbo SIM”, which is a tiny, wafer-thin, SIM-sized printed circuit that goes over the top of the chip on your new MVNO SIM. For unlocking my off-contract au iPhone 4S, I used a Gevey Turbo SIM that I got from Amazon for 710 yen. This is specifically for an iPhone 4—if you have an iPhone 5 or later, you’ll need a Nano SIM chip. The product advertised on Amazon says for “iOS 6”. The package I received said “iOS 8”. My phone had iOS 9 installed, but it still worked.

Unfortunately, the process is not well documented; a link in the Gevey SIM packaging leads to a dead link—which is never encouraging! The following steps worked for me, but I had to try them multiple times before seeing success, so be patient and be prepared to try different combinations or the same thing over and over a few times.

unlocking a japanese iphone
au iPhone 4S, Gevey Turbo SIM in packaging and my IIJmio SIM. | Photo by Greg Lane

Step 1: Remove the old SIM

Look for that funny little key you get with your iPhone to pop out the SIM drawer (a paperclip or the back of an earring works just as well). Pop the drawer out and remove the big carrier SIM and put to one side—you won’t need the little drawer either. You don’t need to switch your phone off and you should make sure you have plenty of battery left.

Step 2: Prepare the Turbo SIM

The Turbo SIM comes with:
i) Its own drawer that is slightly different to the one on your phone
ii) The Turbo SIM—be careful with this. It’s thin and you can break/tear it easily.
iii) Something that looks like a phone SIM but isn’t—a fake SIM



Place the Turbo SIM in the drawer and put the fake SIM provided on top of it. Both of them can be inserted only one way, so it’s impossible to make a mistake. Make sure they both fit in the drawer snugly with no gaps.

unlocking a japanese iphone
Turbo SIM, with drawer, key and old SIM at bottom (before I realized I also needed the fake SIM). | Photo by Greg Lane

Step 3: Insert the Turbo SIM

Insert the drawer from Step 2 into your iPhone. Something that looks like an app will pop up on screen asking you to select your provider—this is the carrier to which your phone is currently locked. Scroll down to select au, Softbank or DoCoMo. Then tap “Accept” on the next screen.

unlocking a japanese iphone
Photo by Greg Lane

Step 4: Remove the fake SIM and put in your new SIM

Pop the drawer out again using your little key, remove the fake SIM, but leave the wafer-thin Turbo SIM in place. Put your new MVNO SIM on top of the Turbo SIM. Once again, make sure they are nice and snug and then insert them into your iPhone. The same screen asking if you would like to unlock your phone will come up—tap “Accept”. You’re now done with the basic set-up.

unlocking a japanese iphone
Photo by Greg Lane

Step 5: Fixing the APN

APN stands for “Access Point Name”—it’s what your phone uses to access the internet. For some reason, the Turbo SIM changes these to a carrier in Hong Kong. You should change these so they match the settings you got from your MVNO provider. In the photo below, you’ll see I changed them to those for my IIJmio SIM.



unlocking a japanese iphone
Photo by Greg Lane

Step 6: Turn on data roaming

For some reason, the phone thinks it is overseas even though you are in Japan with a Japanese SIM—so you need to switch on data roaming. Since I’m using Japanese data with a Japanese provider in Japan, I’m assuming this won’t be charged at international data roaming rates. I’ll update the article when I’ve confirmed my first bill!

Update: The bill was normal—no nasty data roaming rates! Relief!

Added bonus

For the iPhone 4S handset in particular, the BIG carriers further restricted functionality by disallowing its use as a mobile hotspot. With an MVNO SIM, this can be enabled easily—so you can tether it with your laptop or other devices.

Final warning

Just because this worked for me (and plenty of other people), doesn’t mean it will work for you. If you sign up for an MVNO SIM and then find out you can’t use it on your old iPhone, well that’s just a risk you’ll have to take. The Turbo SIMs are super cheap, so if you’re not sure, just buy one and try it with a friend’s SIM.

Last updated in April 2017.

Written by:
Tokyo Cheapo small logo

Watch this next

New Video: Tokyo City Flea Market

Tokyo flea markets are a great for bargain-hunting, pick up a new kimono or snag a new book on a shoestring!




Latest Japan Jobs


Get our Tokyo Cheapo Hacks direct to your inbox





One Response to “Unlocking Your Old Carrier-Locked Japanese iPhone to Use with a Cheap SIM”

  1. sarahsensei

    Hi Greg!

    Interesting and helpful post. Did you get a chance to see how turning on data roaming affected your bill? My contract is up for renewal but I’m thinking about using Asahi Net instead of signing up with a major mobile network.

    I want to keep my old phone number so I figured Asahi Net would be good. Do you know of anyone who has used the Gevey Turbo SIM on an iPhone5c from one of the big 3?


Questions or comments about this article? Start a thread on our community forum